The more than 43,000 Twitter followers of Rosanne Cash, the singer and daughter of Johnny Cash, have come to expect her tart commentary on married life with her husband, John Leventhal, a Grammy-winning musician.

She chided him for performing at a concert in jeans he had worn three days in a row. Another day, she postedthat he had cajoled her to help organize his “stuff.” But Mr. Leventhal, known as Mr. L to Ms. Cash’s followers, apparently is not a fan of her enthusiasm for sharing online.

Ms. Cash said in an interview that another time she wrote about her husband taking a nap. When he showed up at the studio, the sound engineer was puzzled, since he had just read Ms. Cash’s post online. “I thought you were taking a nap,” the engineer said to him.

“John called me and he was really annoyed,” she recalled. “He said, ‘Don’t tell people I’m taking a nap!’ ”

Relationships are hard enough. But the rise of social media — where sharing private moments is encouraged, and provocative and confessional postings can help build a following — has created a new source of friction for couples: what is fair game for sharing with the world?

If one half of a couple is not interested in broadcasting the details of a botched dinner or romantic weekend, Facebook postings or tweets can create irritation, embarrassment, miscommunication and bruised egos.

After a few relationship-testing episodes, some spouses have started insisting that their partners ask for approval before posting comments and photographs that include them. Couples also are talking through rules as early as the first date (a kind of social media prenup) about what is O.K. to share. Even tweeting about something as seemingly innocent as a house repair can become a lesson in boundary-setting.

“There is a standard negotiation that takes place in lots of relationships, but now there are multiple audiences watching,” said Lee Rainie, the director of the Pew Research Center’s Internet and American Life Project, which explores technology and human behavior. “There will be awkward moments, even more so if that negotiation is played out in public.”

Interviews with more than a dozen couples suggest that disagreements over how much to share are common.

Rebecca Gray, a doctoral student at Michigan State in East Lansing, lives with her boyfriend, Ernest Whiting. Last May, Mr. Whiting took a photograph of her face — eyes closed, mouth open wide — slathered in a beauty mask of volcanic mud she bought in Costa Rica.

In August, Ms. Gray was at work and received a notification from Facebook that said she had been tagged in a photo. When she looked at it, she found that Mr. Whiting had retrieved the photo from her computer and posted it on his Facebook account. “My jaw dropped,” she said. “I tried to remove it, but I could only untag.”

She e-mailed and sent a text to Mr. Whiting, demanding he take it down. By then, friends and acquaintances had seen it. “It was showing up in my newsfeed,” Ms. Gray said. “People said: ‘What is this? It is hilarious!’ ” As a last resort, she logged into his account and removed the photo herself. When Mr. Whiting got home that night, Ms. Gray was waiting. “I said: ‘You have lost the privilege of using my computer. What were you thinking?’ ” Ms. Gray recalled.

Mr. Whiting, for his part, said he was just having fun.

“I suppose if I thought about it in context, I wouldn’t have done it,” he said. And he is unlikely to do it again. “She asked for photo approval, and I said yes,” he added sheepishly.

Some couples seek to preserve intimacy by establishing rules early on. Jen Dunlap, who lives in Brooklyn, took a trip to Turks and Caicos in May 2009 with her new boyfriend, Chris Sullivan, an actor and musician. Before they left, she said, Mr. Sullivan asked her not to post photos on Flickr of the couple kissing. “I feel like people don’t want to see it,” Mr. Sullivan said.

But even couples steeped in social media are grappling with the new layer of relationship etiquette. Nozlee Samadzadeh and Jarrett Moran have had active online social presences for years. In 2009, they set up a Tumblr account called Needs More Salt where they post photographs and comment on meals they cook. Ms. Samadzadeh said she once upset Mr. Moran when she joked that he was hapless in the kitchen.

To avoid further conflict, the couple agreed to review each other’s comments before posting. It was a wise move. Recently, Ms. Samadzadeh said that she almost posted a comment on Needs More Salt expressing annoyance at having to make supper because Mr. Moran was home late. Mr. Moran, though, did not know he was supposed to cook and asked her to rewrite the post. “I don’t want to be embarrassed,” Mr. Moran said.

More often, one partner is more eager to share than the other. Two years ago, Jenny Luu, a skin-care specialist from Washington, D.C., said that she asked her husband, Jason Hamacher, a musician and photographer, to stop posting on Facebook when he was away on business. (She didn’t want strangers to know she was home alone.)

The couple also owns a 100-year-old home in a historic neighborhood. Two months ago, Ms. Luu bristled when her husband wrote on Facebook about a second round of repairs to their roof.

For three years Mr. Hamacher had posted comments and photographs about their home renovation. The accumulation of comments made Ms. Luu uneasy, worried that their friends would think they were bragging. “I don’t want people thinking we have so much money, that we are loaded,” Ms. Luu said. “I don’t want to make people uncomfortable.”

For some spouses, though, the best defense is ignorance.

George Stephanopoulos, the former Clinton White House staff member who is now an anchor of “Good Morning America,” said he was named “anchor most likely to be anxious about his wife’s tweets” at ABC News’ 50th-anniversary party in January. He is married to the comedian Alexandra Wentworth, who has more than 42,000 Twitter followers. “I have sort of a simple rule,” Mr. Stephanopoulos said, laughing. “Don’t ask, don’t read.”

Ms. Wentworth usually refrains from posting jokes about politics on Twitter, although she said it was hard to resist during the New Hampshire Republican debate in January that Mr. Stephanopoulos helped moderate. “Honey, stop sexting me and pay attention to the debate!” she wrote.

“I don’t think he saw it,” Ms. Wentworth said later. He hadn’t. (Mr. Stephanopoulos has more than 1.7 million Twitter followers; his posts are mostly work-related.) Nor had he read his wife’s off-color joke about a suspect stain on a certain candidate’s tie. When asked about it, he stopped laughing. “I’m so glad I didn’t know about that,” he said.

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